Pneumatic signal generator



' Unfit-Ed States (Patent? 195cc; J

' 3,399,692 PNEUMATIC SIGNAL GENERATOR Edgar-G. Hustle, Rocln'ille, and'Richard N. Gottron,

Kensington, Md assignors to the United States of America as represented by the Secretary of the Army Filed May 25, 1965, Ser. No. 458,795

8 Claims. (Cl. 137-815) ABSTRACT or "rim DISCLOSURE A piezoelectric crystal is placed in the control channel of a pure fluid amplifier. An electrical signaL'having a frequency equal to the natural frequency of the crystal, is applied to piezoelectric crystal .to control the fluid amplifier. Y t

The invention described herein may be manufactured and used by or for the Government ofthe United States of America for governmental purposes without the payment to us of any royalty thereon. p This invention relates generally to fluid .systems 2 j 2 thus make it possible to have the streams interact in a region at some desired ambient pressure, the side walls are so placed that they are somewhat remote from the high velocity portions of the interaction stream. In the second class of pure fluid amplifiers, the position and shape of the side walls of the interaction region are of utmost importance. The power stream nonnally attaches to one or the-otherof the side walls in the interaction region "due to the well known'Coandaeflect. The power stream maybe switched" betweenthe side walls of the interaction region by deflecting the power stream with a pulsed control .jet. The power stresmwill rcmain-attached to the side wall of the interaction region until another pulsed control jet causes it to deflect again. Such units are commonly referred to as bistable fluid amplifiers.

One of the important advantages of a-pure fiuid system is that the response time of the system is limited only by more particularly to eiectropueumatic signal generators capable ofproducing pneumatic signals having any desired a wave shape over a broad range of frequencies.

In the fields of control and data processing, considerl able research and development have been directed toward 7 pure fluid systems. Pure fluid systems ofier many advantages not otlered by electronic orelectromechanical systems. Notably, they are rugged, simple, inexpensive and immune to radiation. Furthermore, fluids in motion are widely used in military and industrial systems. For examthe speed of sound in the acoustic media employed. .For

' example, the switching me of a bistahle'pneurnatic amplifier has been shown to be on -the order of several hundred microseconds- Such fast response is due to the fact that the systems contain no moving parts. However, in order to switcha system of pure fluid. elements, ithas been heretofore necessary to supply the first unit of the system with a fluid controlsignals-This signal is usually supplied by mcansof a valve. Of course, a valve is a moving part and hence-in practicethe systems developed have not been completely 'free of moving parts. The introduction of moving parts into an otherwisepure fluid system greatly lowersthe reliability and theiresponse time of the system. Thus,'the need is apparent for a way to switch pure fluid systems. without the useof'moving ple, chemical processes, machine tools, rocket motors and many other devices depend upon precise and timelycontrol of'rnoving fluids for proper operation. The heart of any pure fluid system is the pure fluid amplifier. Basically, y la pure fluid amplifier comprises a main fluid nozzle which issues a well-defined power stream into Jan interaction region. Positioned downstream from thepower stream are of the power jet. This pressure differential is used to deflect the power jet so that the power jet will exit. the b interaction region through the desired output channel of the fluid amplifier. Typically a ifluid amplifier is constructed by laminating three plastic plates together, the inner plastic plate being molded or otherwise shaped to form the various fluid passageways and the interaction region of the fluid amplifier.

There are two broad classes of pure fluid amplifiers. The first of these is based on stream interaction or momentum exchange principles. The second is based on boundary layer control or the Coanda effect. In the momentum exchange class of fluid amplifiers, one "or more control streams interact with a power stream to deflect the power stream with little or no interaction between the side walls of the interaction region. Power stream deflection in such a unit is continuously variable in accordance with the control signal amplitude. Such a unit is commonly referred to as a proportional amplifier. In an amplifier of this type, the detailed contours of the side wallsof the interaction region are of secondary importance to the interacting forces between the streams themselves. Although the side walls of such units are used to contain the fluid of the interacting chamber and parts in order to take full advantage of the fast response timcjand high reliability inherent-in these s'ystemsqgir' In additiontothe need for eliminating all moving parts lin fluid amplifier-system's, thewide-sprcaduse'of-elcc tronics in control systems-hascreateda need forpure fluid .elements which can be controlled by electrical input signals." For example, pure. fluid elements connected together to obtain an amplified fluid signal can --be usedv to control a high-speed jet' such as that generatedby a rocket. Ajfluid, element which can becontrolled by anelectrical signal would make it possible to, introduce into the pure fluid system an electrical signal frorna gyroscope or other guidance sensor and deficct by 'secondary iujection methods the main exhaust jet ofithe rocket. In add.- tion, suc h. an element would make possible the interconnecting of fluid elements with the electrical elements in 7 other computer and control applications.

'It is thereforepan object of the present invention to provide a pneumatic signal generator which produces the pneumatic output signal that is proportional to an electrical input signal.

It is another object of this invention'to provide means for controlling the output of the pure fluid amplifier with an input electrical signal that does not materially detract from the response time or the reliability of the pure fluid amplifier.

'It is a further object of the instant invention to provide an electropneumatic transducer which produces an output pneumatic signal that varies in direct proportion to an input electrical signal which may have any arbitrary wave shape and vary over a considerable range of frequencies.

According to the present invention, the foregoing and other objects are attained by providing a pure fluid amplifier which is controlled by the acoustical signal generated by a piezoelectric crystal which is caused to vibrate at its natural resonant frequency by an amplitude mOdtb objects, aspects, uses and advantages thereof,wiil clear- Patented July 2, 1958 I tile 1'...

1y appear from the following dewription and from the accompanying drawing, in which:

FIGURE 1 is a block diagram illustrating a first embodiment of the present invention which uses a pro-, portional pure fluid amplifier,

supplied with fluid by way of channel 13 from a source of fluid under pressure (not shown). The fluid supplied to nozzle IZissues therefrom as awell-defincd power stream into interaction chamber 14. Positioned downto FIGURE 1, there is shown a proportional pure fluid amplifier 11 having a main fluid nozzle 12 Nozzle 12 is.

stream from the power stream is a fluid flow divider 15. t

The walls of the interaction chaIJccrl-i and thewalls of the fluid flow divider l5 define the output channels 16 and l'lrNorrnally with no control. signal the power stream divides evenly between output channels lo and 17. Positioned adjacent to main nozle 12 and perpendicular to the power streamissaing therefrom is a control,

nozzle 18. Control nozzle 18 communicates with a control channel 19. A pressure signal developed in the control channel 19 will cause a portion of a fluid therein to issue from control nozzle 18 as a control jet. This control jet will cause the power stream to deflect. Under these circumstances, the greater portion of. the power stream will exhaustthrough ouzputvchannel l7, thzinj output channel 15, depending upon. the magnitude of the pressure signal developed in control channel '19. Partially extending into control channel 19 is a piezoelectric crystal 21. Piezoelectric crystal 21 is provided with electrodes 22 and 23 .which are plaiedorolherwise bonded to oppositesnriaces thereof. When electrical charges are placed on the opposite surfaces ofv the crystal 21' by applying a 'voltageacross the electrodes 22 and 23, a mechanical stress ispr'oduced in thecrystal perpendicular to the electric field and parallelwith thcaxis of con trol channel 19. This mechanical-stressproduces a very small elongation or contraction of the crystal. 21- depending upon the nature of the electric field. Ii an alternating voltage is applied across the electrodes'22 and 23, the

. piezoelectric crystal 21 will vibrate. For a given magnitude of alternating voltage, the vibrations of the piezoelectric crystal 21 are maximum when the frequency of the alternating voltage is equal to the, natural resonantv frequency of the crystal. The electrical voltage signal applied across electrodes 22 and 23 is generated by amplitude-modulating a continuous wave voltage signal. More particularly, there is provided a'carrier generator 24 nhich produces an output carrier signal 25 that has a frequency equal tothe naturalfresonant frequency of the piezoelectric crystal 21.

This'output signal is applied to a fast input of modulator 26. The second input of modulator 26 .is supplied by signal generator 27 which produces a modulating signal 28. The modulating signal 28 is here illustrated as a sinusoidal wave but may take oaher forms, such as is. example, a triangular wave, a saw-tooth wave, or any arbitrary wave form. Signal generator 27 may be, for example, a laboratory signal generator or an electronic sensor which is connected in a control system. The output signal 29 of modulator 26 is the carrier signal '25 amplitude modulated by the modulating signal 28. This signal 29 is fed to a power amplifier 31 which in turn develops the output voltage which is applied across electrodes 22 and 23. r

In operation, the pneumatic signal generator shown in FIGURE 1 generates a pneumatic signal that issues from output channel 17 of fluid amplifier 11 that is directly proportional'to the modulating signal 28 produced by signal generator 27. This output pneumatic signal is gcneratedbythe deflection of the power stream I vissued from main fluid nozzle 12due to the acoustic I signals generated in control channel 19 by the vibrations of piezoelectric crystal 21. The acoustical signals produced by vibrations of the crystal 21 exactly reproduce the modulating signal 28. Since the vibrations of the crystal 21 vary in amplitude in direct proportion to the.

modulating signal 28 because the'piezoelectric crystal 21 is excited by an alternating carrier voltage which has a requency equal to the natural resonant frequency of the crystal, a maximum electrical to acoustical power I transfer is attained. Thus the system described is highly efficient, requiring a relatively small amount of elec- 1 trical power to control a relatively high power pneumatic signal. Y

I Referring now to FlGURE 2, there is shown a second embodiment of the present invention which uses a bistable pure fluid amplifier 32. Bistable amplifier 32 comprises a main fluid noule 33 which'is supplied withfluid by Way of channel 34 from a source of fluid under pressure (not shown). The fluid supplied to nozzle 33 issues therefrom into interaction region 35. Downstream from fluid nozzle 33 is a fluid flow divider 3631 he walls of interaction region 35 and the walls of fluid flow divider 36 define the output passages 37 and 38. 7 Since the walls of the interaction region 35 are close to the power stream issuing from fluid nozzle'33, the power stream will normally attach to one or the other of the side walls of the interaction region due to the Coanda eflect. Therefore, all of the power stream issuing from nozzle 33 will exhaust through output channel 37 or output channel 38 depending on which of the two side. walls of interaction region 35 the power stream attaches. Positioned adjacent-to the fluid flow nozzle 33 and perpendicular tothe power stream. issuing therefrom is a first control nozzle 39. Fluid control'nozzle SQ'cOmmunicateS- with a first control channel-41. Positioned opposite the first control nozzle 39 is a second control noule 42: This second control nozzle 42-communicates with a second control channel 43. The power stream issuing from'nozzlej33 may be deflected and made to attach on either of the -side walls of interaction region 35 by causing a control -jet to issue irom the appropriate I fluid control nozzle 3901 42. For example, suppose that the power stream is. attached'to the left wallin interaction region 35 and it is desiredthat it be made to deflect and attach to the right wallof interaction regionj35. This may .be accomplished by generating .a fluid pressure signal in gcontrolrchannel 41 which'causes a fluid jet to issuc from control nozzle 39. This control: jet will cause the fluid stream to deflect to the right and in so doing, it will attach to the right side wall of interaction region 35. Should it be desired to cause the power stream to "reattach to the left side wall of interaction region 35, it is merely necessary that a fluid pressure signal be generated in control channel 43. This causes a fluid control jet to issue from control nozzle'42, causing the power stream to deflect to the left.

A piezoelectric crystal 44 is positioned'to' extend partiz ly into control channel 41 in the same manner-that crystal 21 was positioned to extend into control channel 19 in FIGURE 1. A pair of electrodes 45 and 46 are bonded to opposite faces of the piezoelectric crystal 44. Similarly, a piezoelectric crystal 47 is positioned to partially extend into control-channel 43 and electrodes 48 and 49 are bonded to opposite faces of the crystal 47. Piezoelectric crystal 44 generates an acoustical signal in control channel 41 when an alternating electrical voltage is impressed across the electrodes 45 and 46. In a similar manner, piezoelectric crystal 47 will generate an acoustical signal in control channel 43 when an alternating voltage is impressed across the electrodes 48 and 49. The alternating electrical voltages which are applied to piezoelectric crystals 44 and 47 are generat d by gating a continuous wave voltage signal. More partiflarly, a carrier generator 51 is provided to generate an alternating voltage signal 52 having a frequency equal to they natural resonant freoutput. The square wave 55 controls the gating switch and causes it to transmit the continuous wave signal 52 ,to the firstv output during the first half of the square wave signal into the second output during the second half of the square wave signal. This results in first and second 7 output signals 56 and 57. Output signal 56 is applied as the input signal to power amplifier 58 which produces .a voltage signal across the electrodes 45 and 46. The output v signal 57 is supplied as the input signal to power amplifier 59 which produces an output voltage across electrodes 48 and 49.

In the operation the pneumatic signal generator of the embodiment shown in FlGURE 2 produces a. pulsed output pneumatic signal which varies directly as the square wave signal 55. The voltages applied across the FIGURE 3 produces an output pneumatic signal from bi electrodes 45-. and 46 and electrodes 48 and 49 by power amplifiersSSfand 59, respectively, cause the piezoelectric crystals 44 and d7, respectively, to produce alternate acoustical pulses in their respective control channels 41 and 43. These acoustical pulses cause control jets to issue from control noules 39 and 42, respxtively. Since the control jets are in the form of alternate pulses, the power stream issuing fromfluid nozzle 33 is caused to deflect back and forth between output channels 37 and 38.

FIGURE 3 illustrates a modification to the embodiment shown in FIGURE 2 that requires only one piezoelectric crystal and one power amplifier. This modification uses a bistable pure fluid amplifier 61 as before. The amplifier 61 has a main fluid nozzle 62 which is supplied by way of tluidchannel 63 with a fluid under pressure. The

fluid supplied to the main nozzle 62 issues as a power jet into reaction region 64. The side walls ofireaction region .64 together with the side walls of the fluid flow divider 65 positioned downstream from the fluid nozzle 62'de'fine output channels 66 and'67. The power stream exhausts through either channel or channel 67 depending on which ofthe side walls of the reaction region'the' power jetattaches. Located adjacent to the nozzle'62fandtransj verseto the power stream issuing therefrom are control nozzles 68 and 69. Control nozzles 68 and 69 communicate l with control channels 71 and 72, respectivdyQTheoutput channel 67 is connected by way of a pneumatic delay-73 to control channel 72. If thepovver stream issuing from nozzle 62 is deflected into outputchannel 67 by a control jet developed by a pressure signal in control channel 71, a pneumatic pressure signal will be transmitted to delay 73. After a period of time, depending upon the capacity of delay 73, this pneumatic pressure signal appears in control channel 72. As a result, a control jet is caused to issue from control nozzle 69 and produces the deflection of the power stream issuing from the nozzle 62 into output channel 66.

A piezoelectric crystal 73 is positioned to partially extend into control channel 7!. Electrodes Hand 75 are bonded to opposite faces of the piezoelectric crystal 73. The electronic circuitry that produces the voltage across the electrodes 74 and 75 is essentially the same as that shown in FIGURE 2. This includes a carrier generator 76 which produces an alternating output voltage signal 77. This signal 77 is supplied as the first input to gating switch 78. The square wave generator 79 which produces an output square wave 81 provides the second input to gating switch 78. The gating switch 78 is essentially the same as gating switch 53 in FIGURE 2 except that it produces only one output. This output is in 'the form of a gated carrier signal 82 which is supplied as the input to power amplifier 83. The power amplifier 83 pro duces an output voltage which is applied across electrodes 74 and 75.

In operation, the pneumatic signal generator shown in generator producing a variable voltage signal having a I stable pure fluid amplifier 61 which closely approximates the square wave 81. The acoustical pulses produced by the piezoelectric crystals 73 cause pulsed control jets to issue from control nozzle 68;[hese pulsed control jets cause i the power stream issuing from nozzle '62 to defiect into output channel 67. A portion of the power stream ex-, hausting through output channel 67 is fed back to the control channel 72 by way of a pneumatic delay 73.

Thus, after the power stream has been deflected into chan nel 67, it is caused to deflect back into channel-66 by I the delayed output signal in channel 67. The next pulse produced by the piezoelectric crystal 73 causes the power stream to again deflect into output channel 67. Since the period of time that the power stream exhausts through output channel 67 is dependent upon the characteristics of thepneumatic delay 73, the output pneumatic signal from 'the amplifier 61 will be directly proportional to the square wave 8i only when the delay characteristics of delay 73 are equal to a half a periodof the square wave 81. I

It will be apparent that the embodiments shown' are only exemplary and that various modifications can be a fluid flow divider positioned downstream from said. Q

I main fluid nozzle,

the wallsof said interaction region and said fluidifiow divider defining at least two output channels, a control channel and a control nozzle positioned adjacent to said main flow nozzle and perpendicular to a power stream issuing therefrom, said control nozzle communicating withsaid control channel,

a. piezoelectric crystal partially extending into said I contror channel,

j first and second electrodes bondedto'opposite faces I of said piezoelectric crystal,

means for developing a continuousywave alternating.v

' current voltage signal having a frequency equal to the natural resonant frequency of said piezoelectric -crystal, I means receiving said alternating curernt voltage sign'al and varying the amplitude thzzecf,

means for applying the variable amplitude alternating current voltage signal to said first and second elec trodes,

whereby the alternating current voltage signal applied across said first and second electrodes causes said piezo electric crystal to vibrate and produce acoustic pressure signals which vary inamplitude, said power stream being caused to deflect by control jets issuing from said control nozzle due to said variable amplitude acoustical pressure.

2. A pneumatic signal generator as recited in claim 1,

wherein said means for applying the variable amplitude alternating current voltage signal to said first and second electrodes is a power amplifier.

3. A pneumatic signal generator as recited in claim 2,

' wherein said means for varying the amplitude of said continuous wave alternating current voltage signal comprises: a modulator which receives the output from said beams for developing a continuous wave alternating current voltage signal, and a source of modulating voltage connected to said modulator for causing said modulator to vary the amplitude of said continuous wave alternating current voltage signal.

4. A pneumatic, signal generator as recited in claim 3,

wherein said source of modulating voltage is a signal desired wave shape.

wherein said means for varying the amplitude of the con- 2 square wave generator connected to said gating switch and causing said gating switch to transmit said altertinting curent voltage signal to said means for applying the voltage signal to said first and secondelectrodes only during one-half the period of the output j of said square wave-generaton 6. A pneumatic signal generator as recited in claim 5, @wherein'snid pure fluid amplifier has a second control channel and a second control nozzle positioned adjacent said main fluid nozzle perpendicular to a power stream issuing therefrom and opposite the first control nozzle, said second control nozzle communicating with said second control channel, and comprising? i a second piezoelectric crystal partially extending into said second control channel, 7 i third and fourthelectrodes bondedto op; Jsite faces of said second piezoelectric crystnLand second means connected to said gating switch for applying an alternating current voltage signal to said second crystal which is the complement of the alternating current voltage signal applied to said first piezoelectric crystal. I 7. A pneumatic signal generator as recited in claim 5, wherein said pure fiurd amplifier additionally has :r secondcontrol channel,

a second control nozzle positioned adjacent said main fluid nozzleperpendicu'lar to a power stream issuing therefrom and opposite the first control nozzle, said second control communicating with said second control channel, and g ,7 g a pneumatic delay means connected to an output chan- .tie] and said second control channel for producing a delayed pneumatic. pressure signal 'insaid second control channel'thereby causing a control jet to issue fromsaid'second conrrolnozzle causing the deflection of a power stream issuing frornsaid main fluid nozzle. j' v S, A pneumatic signal generator comprising: a pure fluid amplifier having amain fluid noule,

aminteraction. region positioned to receive a power 4a gstream issuing from said main fluid nozzle, a fluid flow divider: positioned downstream from said sure.

, References Cited UNITED STATES PATENTS 2,894,123 7/1959 Hansel] .-.325181 X r 3,100,886 8/1963 Marks 625-37 X 3,121,169 .2/1964 Benton 250-199 3,122,062 2/1964 Spivak et al. 137-815 X 3,144,037 8/1964 Cargill et a1. 137-815 3,158,166 11/1964 Warren 137-815 3,182,686 5/1965 'Zilberfarb 137--81.5 X 3,187,762 6/1965 'Norwood 137- 81.5 3,266,511 v8/1966 Tnrick 137-815 3,269,419 8/1966 Dexter 137-815 9/1966 Meier 137-415 SAMUEL sco'rr, Primary Examiner.

spect to said main fluid nozzle,

the walls of said interaction region and said fiuidilow divider defining at leasttwo output channels, a control channel and a control nozzle positioned ad- 7 jacent to said main flow nozzle and perpendicular to a power stream issuing therefrom, said control nozzle communicating with said control channel,

, a piezoelectric crystal partially extending into saidcon trol channel,

of said piezoelectric crystal, means for developing a continuous wave alternating current voltage signal having a frequency equal to the natural resonant frequency of said piezoelectric crystal,

means receiving said alternating current voltage signal and varying the amplitude thereof,

' means for applying the varinbleamplitude alternating current voltage signal) to said first and second elecnozzle-due to said variable amplitude acoustical pres- M; CARY NELSON, Examiner;

main fluid nozzle and symmetrically placcdwith-refirst and second electrodes bonded to opposite faces 

